Something I'm playing around is the 4e genasi's ability to gain multiple manifestations and even have two active at the same time through the elemental tempest paragon path. There are two ways I can think of to do this, either through feats or through a class. Since I had the inspiration for it, I decided to start with the class. In addition to the additional subrace, they also gain limited spellcasting ability and learn to channel some elemental spells as a means to represent their increased control over the elements.
Some starting notes. It is only 5 levels, it does not gain subclass abilities. Because it can be taken at 1st level, they have the full features of a starting class including proficiencies and saving throws. Although most inborn casting ability is modelled on Charisma, I decided to run with Intelligence as Genasi gain a racial bonus to this ability and this class represents expanding their racial powers.
For a spell list, assume any spell dealing with elemental energies is on the list (fire, air, lightning, thunder, cold, acid, earth, water, etc)
I could actually see this being a fully fledged class with subclasses based on specific elements, but I have kept it at 5 levels
Elemental Tempest
You are as inconstant as the wind on the sea, and yet you burn with passions to match a dragon’s ire. You embrace the chaos from which your people were born. Fire to blacken adamantine, water to wash away an armada, wind to freeze a dragon in flight, and lightning to blast a castle to rubble all flow through your spirit. You are a force of nature incarnate.
Some genasi work to expand their connection to the elements becoming elemental tempests. Early on they learn to shift in and out of different elemental aspects before finally combining the power of disparate elemental energies in their single mortal form.
Class Features
Hit Points
Hit Dice: 1d8 per elemental tempest level
Hit Points at 1st Level: 8 + your Constitution modifier
Hit Points at Higher Levels: 1d8 (or 5) + your Constitution modifier per elemental tempest level after 1st.
Proficiencies
Armour: light armour
Weapons: Simple weapons
Tools: None
Saving Throws: Constitution, Intelligence
Skills: Choose two from Athletics, Arcana, Insight, Intimidation, Nature, Perception, and Survival
Multiclassing
Genasi who wish to pick up the abilities of the elemental tempest after 1st level must have an intelligence of at least 13. They gain the following proficiencies: light armour, simple weapons.
[TABLE="width: 60%, align: left"]
[TR]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD="colspan: 2"][/TD]
[TD="colspan: 3"]
Spell Slots[/TD]
[/TR]
[TR]
[TD]
Level[/TD]
[TD]
Prof. Bonus[/TD]
[TD]
Special Abilities[/TD]
[TD]
Cantrips Known[/TD]
[TD]
Spells Known[/TD]
[TD="colspan: 2"]
1st[/TD]
[TD]
2nd[/TD]
[TD]
3rd[/TD]
[/TR]
[TR]
[TD]
1[/TD]
[TD]+2[/TD]
[TD]Dual Soul, Spellcasting[/TD]
[TD]2[/TD]
[TD]4[/TD]
[TD="colspan: 2"]2[/TD]
[TD]-[/TD]
[TD]-[/TD]
[/TR]
[TR]
[TD]
2[/TD]
[TD]+2[/TD]
[TD]Elemental Recovery[/TD]
[TD]2[/TD]
[TD]5[/TD]
[TD="colspan: 2"]3[/TD]
[TD]-[/TD]
[TD]-[/TD]
[/TR]
[TR]
[TD]
3[/TD]
[TD]+2[/TD]
[TD]Dual Manifestation[/TD]
[TD]2[/TD]
[TD]6[/TD]
[TD="colspan: 2"]4[/TD]
[TD]2[/TD]
[TD]-[/TD]
[/TR]
[TR]
[TD]
4[/TD]
[TD]+2[/TD]
[TD]Ability Score Increase[/TD]
[TD]3[/TD]
[TD]7[/TD]
[TD="colspan: 2"]4[/TD]
[TD]3[/TD]
[TD]-[/TD]
[/TR]
[TR]
[TD]
5[/TD]
[TD]+3[/TD]
[TD]Elemental Rejuvenation[/TD]
[TD]3[/TD]
[TD]8[/TD]
[TD="colspan: 2"]4[/TD]
[TD]3[/TD]
[TD]2[/TD]
[/TR]
[/TABLE]
Spellcasting
Spellcasting Ability is Intelligence.
Elemental Focus: The elemental energies within you are the focus for your spells. You do not require material components for your elemental tempest spells unless the material component has a gold cost.
Dual Soul
At 1st level, choose another genasi subrace. During a long rest, you may choose which element to manifest until your next long rest. You gain all of the abilities of that element while it is manifested. The Ability Score Increase you gain from the subrace is permanent and doesn’t change when you swap elements.
Elemental Recovery
At 2nd level, during a short rest, you may regain spent spell slots with a total combined level equal to half your Elemental Tempest level (rounded up).
Once you use this ability, you cannot use it again until you have completed a long rest.
Dual Manifestation
At 3rd level, your increasing control over your elemental soul enables you to manifest both of your chosen elements. You gain all of the abilities of both elements with the following restriction: You may use only a single elemental daily power per long rest, you may choose which to use when you activate it.
The elemental daily powers for each subrace are:
earth shock, fire pulse, promise of storm, swiftcurrent, windwalker, acid surge, firedeath, plaguebearer, and void assumption.
Elemental Rejuvenation
At 5th level, during a short rest, you may regain your elemental manifestation power.
Once you use this ability, you cannot use it again until you have completed a long rest.